Business Segment Information - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Noninterest income:
Fixed income	$ 46,000	$ 96,000	$ 170,000	$ 324,000
Deposit transactions and cash management	43,000	44,000	129,000	130,000
Brokerage, management fees and commissions	23,000	24,000	71,000	65,000
Mortgage banking and title income	9,000	34,000	65,000	126,000
Card and digital banking fees	21,000	21,000	64,000	59,000
Other service charges and fees	13,000	12,000	41,000	32,000
Trust services and investment management	11,000	13,000	36,000	39,000
Securities gains (losses), net	12,000	1,000	18,000	12,000
Deferred compensation income	(3,000)	3,000	(24,000)	12,000
Loss on debt extinguishment	0	(23,000)	0	(23,000)
Other income	38,000	22,000	72,000	53,000
Total noninterest income	213,000	247,000	642,000	829,000
Underwriting, portfolio advisory, and other noninterest income
Noninterest income:
Revenue from contract with customer	13,000	12,000	33,000	35,000
Regional Banking
Noninterest income:
Fixed income	0	0	0	1,000
Deposit transactions and cash management	39,000	40,000	115,000	117,000
Brokerage, management fees and commissions	23,000	24,000	71,000	65,000
Mortgage banking and title income	0	0	0	0
Card and digital banking fees	19,000	18,000	57,000	51,000
Other service charges and fees	8,000	6,000	24,000	18,000
Trust services and investment management	11,000	13,000	36,000	39,000
Securities gains (losses), net	0	0	0	0
Deferred compensation income	0	0	0	0
Loss on debt extinguishment		0		0
Other income	10,000	12,000	34,000	32,000
Total noninterest income	110,000	113,000	337,000	323,000
Specialty Banking
Noninterest income:
Fixed income	46,000	96,000	170,000	323,000
Deposit transactions and cash management	2,000	3,000	7,000	8,000
Brokerage, management fees and commissions	0	0	0	0
Mortgage banking and title income	9,000	34,000	65,000	124,000
Card and digital banking fees	0	1,000	2,000	2,000
Other service charges and fees	5,000	5,000	17,000	12,000
Trust services and investment management	0	0	0	0
Securities gains (losses), net	0	0	0	0
Deferred compensation income	0	0	0	0
Loss on debt extinguishment		0		0
Other income	2,000	3,000	4,000	8,000
Total noninterest income	64,000	142,000	265,000	477,000
Corporate
Noninterest income:
Fixed income	0	0	0	0
Deposit transactions and cash management	2,000	1,000	7,000	5,000
Brokerage, management fees and commissions	0	0	0	0
Mortgage banking and title income	0	0	0	2,000
Card and digital banking fees	2,000	2,000	5,000	6,000
Other service charges and fees	0	1,000	0	2,000
Trust services and investment management	0	0	0	0
Securities gains (losses), net	12,000	1,000	18,000	12,000
Deferred compensation income	(3,000)	3,000	(24,000)	12,000
Loss on debt extinguishment		(23,000)		(23,000)
Other income	26,000	7,000	34,000	13,000
Total noninterest income	$ 39,000	$ (8,000)	$ 40,000	$ 29,000